[PATCH v2] MIPS: dts: loongson64g-package: Switch to Loongson UART driver

[PATCH v2] MIPS: dts: loongson64g-package: Switch to Loongson UART driver

[Rong Zhang]

Loongson64g is Loongson 3A4000, whose UART controller is compatible with
Loongson 2K1500, which is NS16550A-compatible with an additional
fractional frequency divisor register.

Update the compatible strings to reflect this, so that 3A4000 can
benefit from the fractional frequency divisor provided by loongson-uart.
This is required on some devices, otherwise their UART can't work at
some high baud rates, e.g., 115200.

Tested on Loongson-LS3A4000-7A1000-NUC-SE with a 25MHz UART clock.
Without fractional frequency divisor, the actual baud rate was 111607
(25MHz / 16 / 14, measured value: 111545) and some USB-to-UART
converters couldn't work with it at all. With fractional frequency
divisor, the measured baud rate becomes 115207, which is quite accurate.

Signed-off-by: Rong Zhang <rongrong@oss.cipunited.com>
---
This patch targets the MIPS tree.

The series for the serial tree to update dt-bindings and enable building
8250_loongson (loongson-uart) on MIPS Loongson64 is sent separately, as
it's independant of this patch and can be applied in any order (the
compatible strings here still contain "ns16550a", so no regression will
be introduced).

Changes in v2:
- Separated from v1 (patch 3): https://lore.kernel.org/r/20260314234143.651298-1-rongrong@oss.cipunited.com/
(thanks Krzysztof Kozlowski)
---
 arch/mips/boot/dts/loongson/loongson64g-package.dtsi | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/boot/dts/loongson/loongson64g-package.dtsi b/arch/mips/boot/dts/loongson/loongson64g-package.dtsi
index d4314f62ccc2..029daeedd0ab 100644
--- a/arch/mips/boot/dts/loongson/loongson64g-package.dtsi
+++ b/arch/mips/boot/dts/loongson/loongson64g-package.dtsi
@@ -40,7 +40,7 @@ liointc: interrupt-controller@3ff01400 {
 		};
 
 		cpu_uart0: serial@1fe00100 {
-			compatible = "ns16550a";
+			compatible = "loongson,ls3a4000-uart", "loongson,ls2k1500-uart", "ns16550a";
 			reg = <0 0x1fe00100 0x10>;
 			clock-frequency = <100000000>;
 			interrupt-parent = <&liointc>;
@@ -50,7 +50,7 @@ cpu_uart0: serial@1fe00100 {
 
 		cpu_uart1: serial@1fe00110 {
 			status = "disabled";
-			compatible = "ns16550a";
+			compatible = "loongson,ls3a4000-uart", "loongson,ls2k1500-uart", "ns16550a";
 			reg = <0 0x1fe00110 0x10>;
 			clock-frequency = <100000000>;
 			interrupts = <15 IRQ_TYPE_LEVEL_HIGH>;

base-commit: 267594792a71018788af69e836c52e34bb8054af
-- 
2.53.0

Re: [PATCH v2] MIPS: dts: loongson64g-package: Switch to Loongson UART driver

[Thomas Bogendoerfer]

On Mon, Mar 16, 2026 at 02:44:00AM +0800, Rong Zhang wrote:
> Loongson64g is Loongson 3A4000, whose UART controller is compatible with
> Loongson 2K1500, which is NS16550A-compatible with an additional
> fractional frequency divisor register.
> 
> Update the compatible strings to reflect this, so that 3A4000 can
> benefit from the fractional frequency divisor provided by loongson-uart.
> This is required on some devices, otherwise their UART can't work at
> some high baud rates, e.g., 115200.
> 
> Tested on Loongson-LS3A4000-7A1000-NUC-SE with a 25MHz UART clock.
> Without fractional frequency divisor, the actual baud rate was 111607
> (25MHz / 16 / 14, measured value: 111545) and some USB-to-UART
> converters couldn't work with it at all. With fractional frequency
> divisor, the measured baud rate becomes 115207, which is quite accurate.
> 
> Signed-off-by: Rong Zhang <rongrong@oss.cipunited.com>
> ---
> This patch targets the MIPS tree.
> 
> The series for the serial tree to update dt-bindings and enable building
> 8250_loongson (loongson-uart) on MIPS Loongson64 is sent separately, as
> it's independant of this patch and can be applied in any order (the
> compatible strings here still contain "ns16550a", so no regression will
> be introduced).
> 
> Changes in v2:
> - Separated from v1 (patch 3): https://lore.kernel.org/r/20260314234143.651298-1-rongrong@oss.cipunited.com/
> (thanks Krzysztof Kozlowski)
> ---
>  arch/mips/boot/dts/loongson/loongson64g-package.dtsi | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

applied to mips-next

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]